There are three primary steps involved in post-processing
planetary images (or any astronomical images, for that matter). They are

1. Stacking and averaging
2. Sharpening
3. Adjusting levels

The second and third options will be familiar to anyone
who has ever used an image editing program like Photoshop. The Unsharp
Mask filter is a miracle of digital photography. However, the stacking
process may need a bit more of an explanation.

How does the stacking process work?

1. A single raw image from a run of 100. I
selected one of the clearer ones for this example. The first step in processing
is to eliminate all unacceptable images from the run. This means images
blurred by excessive atmospheric shimmering or by vibration of the telescope.
In this case, I eliminated all but 27 images, which are combined, or stacked
for step 2.

2. The 27 best images from the original 100, now stacked
together. The basic idea behind stacking is to make a sandwich with
multiple pictures of the same object to boost the faintest details and
their color saturation while the graininess of the picture and other
defects are greatly reduced.

Note that the stack in step 2 appears blurrier than the individual
frame above. This is only temporary as the 2nd image contains much more
information than the single frame, and is ready now for additional post
processing.

3. The stack after an initial round of processing. The
primary mode of processing is sharpening, which can be done by most
image manipulation programs such as Photoshop. The sharpening process
brings out the wealth of detail provided by the stacking step, and produces
an image composite far better than any of the individual frames.

Other processing steps could include adjusting brightness and contrast,
as well as RGB levels to enhance the colors and bring out detail in
the rings and clouds.

It's all about signal-to-noise ratio. Stacking multiple
images multiplies the amount of signal present in the composite, but it
also multiplies the noise. However, signal (actual physical features visible
on the planet) increases at a higher rate, or co-adds. Noise is random
(caused by atmospheric refraction, vibrations of the telescope, etc.)
and thus it grows at a much slower rate. Thus a stack will always contain
more good information (because signal co-adds) and less spurious info
(signal-to-noise ratio will always increase), than any individual photo.